In general, a method for separating microparticles includes chromatography, sieving, field-flow fractionation (fff), etc. The sieving indicates a method for separating particles using differences in particle sizes. In the sieving, when liquid including microparticles is dropped on the surface of the sieve, particles may be separated into fine or undersize particles (which pass through sieve openings on the surface of the sieve), and coarse, oversize, or tail particles (which stay on the sieve without passing through the sieve openings). Herein, when the above method employs only one sieve, only unsized fractions with unknown particle size distribution are obtained. In other words, only when the particle size distribution of the relevant material is known, it is possible to know the minimum particle size of the undersize particles and the maximum particle size of the oversize particles. On the other hand, in the case where multiple sieves with different-sized sieve openings are provided in a size order, as material passes through each sieve, different-sized portions are obtained, and herein, maximum and minimum particle sizes of each portion are determined by each sieve opening size. There are patent publications regarding a method for separating microparticles using a sieving method as described above, which include U.S. Pat. No. 6,596,112, invented by Ditter, U.S. Pat. No. 4,256,693 invented by Kondo and Kitajima, U.S. Pat. No. 4,477,575 invented by Vogel, U.S. Pat. No. 5,139,685 invented by De Castro, etc. However, in such a conventional sieving method, it cannot be said that required particle sizes are clearly separated because there is a probability that rod-shaped particles pass through smaller sieve openings, and the respective sieve openings can have unequal sizes. In addition, in the conventional sieving method, a multi-layered sieve is required, and especially, a sieve for analyzing microparticles is required to be precisely manufactured. Accordingly, there has been a problem in that the manufacture is complicated, and high cost is required.
On the other hand, field-flow fractionation, that is, a method for separating colloids, particle material, and polymers, and estimating the size distribution of the same, was originally theorized by J. Calvin Giddings in 1966. In separating of polymers and minute colloid particles, a quick and selective method was required, and also, in liquid chromatography, it was required to minimize adsorption or shear degradation of a test sample in a stationary phase. Therefore, the field-flow fractionation was developed. The separation by the field-flow fractionation is similar to the chromatography in terms of the principle of using an elution technology, but does not require a stationary phase. In addition, the field-flow fractionation is referred to as one-phase chromatography because a moving phase of the test sample is distributed with different speed ranges within a channel. The range of the test sample, which can be separated by the field-flow fractionation, is about 103˜1014 of molecular weight, and is within about 100 μm of particle size. As such a test sample, various materials widely spread over industries, such as biomaterials including protein, liposome, all kinds of polymer (organic or water-soluble) and latex particles, metal particles, paint particles, and particles related to environmental pollution, can be utilized. There are patent publications regarding the field-flow fractionation, which include U.S. Pat. No. 5,160,625 invented by Jonsson and Carlshaf, and U.S. Pat. No. 4,894,146 invented by Giddings, etc. The channel used for the field-flow fractionation has a shape of a narrow tube with a rectangular cross section, which is formed by inserting a spacer between two flat plates and engaging them with each other. The fractionation is performed by interacting parabolic flow between the two surfaces with external field perpendicular to the flow. In other words, in the field-flow fractionation, the force applied from the outside is driving force for the fractionation. When the external field is applied, a test sample within a channel moves toward an accumulation wall, and at the same time is carried toward the flow from the accumulation wall by Brownian diffusion. Therefore, both movements are mutually balanced, and the test sample is in a steady state in a position very close to the accumulation wall. Herein, small particles are more widely diffused than large particles, and thus are in equilibrium in a higher position from the accumulation wall in the channel. Due to the characteristic of the parabolic flow, the small particles in a relatively high-speed flow move at a high speed. Therefore, small particles are eluted first, and then large particles are eluted later. The above described mode is called a normal mode, which is a typical operation mode of the field-flow fractionation. On the other hand, particles of a size larger than 1 μm are hardly influenced by Brownian diffusion. Herein, large particles have a higher central position than that of small particles, and thus are carried by a high-speed flow. Therefore, the separation order is the reverse of the normal mode. Such an operation phenomenon is called a steric mode. The field-flow fractionation is classified into a variety of subtechniques according to a type of an external field or driving force, such as sedimentation field-flow fractionation (fff) using centrifugal force, flow fff using secondary flow, thermal fff using thermal diffusion with temperature differences, electrical fff using an electric field, etc. Herein, physical characteristics of a test sample, such as molecular weight, strokes radius, density, electrical properties, thermal diffusion coefficient, etc. may be optionally utilized. In addition to such operational variety, in the field-flow fractionation, it is possible to easily, quickly and exactly adjust the stay of a test sample by appropriately adjusting the strength of an external field, and also, it is theoretically possible to estimate the stay by calculating flow speed, and the strength of the field applied to the test sample. Also, field-programming for gradually decreasing the strength of the external field allows effective separation of a test sample with wide size-distribution. Also, in such a method, an eluted sample is not destroyed. Accordingly, the test sample, which has passed through a detector, may be collected as narrow fractions, and then, may be used for a secondary analysis using other analysis mechanisms including a microscope, elementary analysis, etc. However, due to the structure characteristics in the field-flow fractionation, an external field of very high strength may interact with biomaterials. In addition, the fractionation is not economical because the manufacturing of a channel is not easy, and an additional device for generating an external field is required.
In order to solve the above-mentioned problems, a channel having a surface topology was manufactured, and a sample including various sized microparticles was filtered. As a result, it was found that the various-sized microparticles are sequentially separated by the surface topology.